1. Field of the Invention
The present invention relates to an outer-rotor permanent magnet (PM) type electric rotating machine that consists of a stator having radially arranged poles with coils wound thereon and rotatably supporting a rotation axis, and a rotor arranged around the stator and holding a permanent magnet facing the poles.
2. Prior Art
Such an outer-rotor PM type electric rotating machine is disclosed in Japanese Patent Laid Open Publication No. 2001-275284, for example. The publication discloses a construction where a single-piece stator core, which is formed by a ring-shaped yoke portion and pole portions extended radially from the yoke portion, is fixed to a bearing housing with bolts as a prior art.
On the other hand, the publication discloses a construction where a separate-type stator core, which is formed by connecting separate poles to a ring-shaped yoke, is fixed to a bearing housing with bolts as an embodiment. Each of the poles has a projection formed at a base portion thereof and the yoke has channels extended in an axial direction. The poles are fixed to the yoke by fitting the projections to the channels, respectively.
However, the single-piece construction of the poles and the yoke described as the prior art in the publication exacerbates utilization efficiency of material and increases difficulty of winding operation of coils. On the other hand, the separate construction of the poles and the yoke increases a component count and the steps of working process.
An object of the present invention is to solve the above described problems of the conventional machines and to provide an improved PM-type electric rotating machine that can increase the utilization efficiency of material, decreases difficulty of winding operation of coils and decreases the component count in comparison with the prior art.
A PM-type electric rotating machine of the present invention comprises a rotation axis, a rotor that rotates together with the rotation axis and a stator that rotatably supports the rotation axis. The rotor has a closed-end-cup-shaped holder that is mounted at one end of the rotation axis and a permanent magnet fixed on an inner surface of a cylindrical portion of the holder. The stator has a housing bush that supports the rotation axis in an axis hole formed through the center thereof, stator cores that are radially mounted around the housing bush to face the outer tip ends thereof to the permanent magnet with an air gap, and coils that are wound around the stator cores via insulators. Inner base portions of the stator cores are connected to one another with pressure so as to form a ring-shaped yoke by mounting the stator cores around the housing bush.
With this construction, since the stator core is formed as separated blocks, the utilization efficiency of material becomes higher.
Further, the coil can be wound around the separated stator core before the stator core is mounted on the housing bush, which improves winding space factor, providing a compact and high-power rotating machine. Furthermore, the stator cores, which are equivalent to the poles in the prior art, are directly fixed to the housing bush without a yoke, which eliminates the need for the yoke and the bolts that fix the yoke to the housing bush, decreasing the component count in comparison with the prior art.
In order to fix the respective stator cores to the housing bush, a reentrant extending in the axial direction maybe formed on the inner surface of each stator core and external protrusions may be formed around the housing bush. In such a case, the stator cores are fixed to the housing bush by fitting the external protrusions to the reentrants and caulking the external protrusions to cause plastic deformation. This construction shows strong fixing strength of the stator cores and enables appliance to a large-torque electric rotating machine.
In addition to the above constitution, a circuit board that carries a drive circuit for the electric rotating machine can be mounted. In this case, the circuit board is preferably fixed to the outer surface of the housing bush by fitting the housing bush to a mounting hole formed on the circuit board.
Further, flat portions may be formed along an inner edge of the mounting hole of the circuit board and an outer surface of a circuit-board-mounting portion of the housing bush so that the circuit board is positioned and fixed to the housing bush by engaging the flat portions with each other. Engagement of the flat portions positions the circuit board and prevents a slip of the circuit board.
An element such as a hall element to detect excitation timing may be installed on the circuit board. Since the hall element can be accurately positioned, torque pulsation is suppressed, which will provide a low-vibration, low-noise and stable electric rotating machine.
In addition to the above constitution, a bracket, which acts as a mounting member of the electric rotating machine to fix the machine to an outside, can be attached.
In this case, the bracket is preferably fixed to the outer surface of the housing bush by fitting the housing bush to a mounting hole formed on the bracket. Further, nicks may be formed along an inner edge of the mounting hole of the bracket. The nicks are outwardly extended from the inner edge. In such a case, after fitting the bracket and the housing bush, a bracket-mounting portion of the housing bush is caulked to cause plastic deformation so that the deformed bracket-mounting portion gets into the nicks. With this fixing construction, the bracket can be strongly fixed to the housing bush without using screws or the like.
Further, the housing bush is preferably formed by die-casting of zinc or aluminum, or sintering molding of sintering material so that manufacturing after die-casting or molding is unnecessary.